I think the cop was more concerned about the possibility of a lone shooting.
You keep claiming this. But if the officer was CALLED for a report of a man carrying a rifle, and the officer was afraid, why did he try to sneakily walk up and just grab the gun, a move which is the most likely to lead to a bad outcome? He had a second cop, why not wait for that cop to be ready, pull weapons, yell to the man to halt, put his hands up, and then tell the man you are going to take his gun?
Let’s turn this around. What if that cop had been like that cop in California, the one who had killed a bunch of people and was on the run? You going to let that cop just walk up to you and disarm you? Then he can kill you easily.
Does a citizen have no presumptive right to protect himself from a police officer who may well be a murderer?
Or do you assert that police can’t possibly be criminals, and therefore the man had absolutely no reason to have any fear of a cop blindly grabbing his gun without warning?